The conventional oscillator of a mechanical wristwatch is the sprung balance. This type of solution has several advantages:                very precise chronometry because of the active length of the balance spring, and its high stiffness in every degree of freedom except one (the rotation of the collet about the virtual centre) and the adjustability of the equilibrium of the balance (all the inertia is concentrated in this component);        stability against external disturbances owing to the relatively high inertia of the balance;        the possibility of maintaining the system by several escapement systems;        the possibility of offsetting thermal variations relatively well;        a relatively high quality factor, even for very low frequencies (from 2 to 10 Hz), and thus low energy consumption, and a large power reserve;        the possibility of working with high amplitudes.However, it also has the following undesirable features:        pivoting, friction, and the plays of the balance staff produce differences in chronometry in the different positions of the watch;        pivoting during rotation makes the quality factor and chronometry dependent on the tribology of the components, which also results in a risk of drift in amplitudes and rates over time;        the requirement for perfect lubrication to optimize pivoting, which introduces an uncontrollable parameter, which can change over time or with differences in temperature and humidity;        the difficulty in maintaining oscillations when the oscillation frequency becomes high, above 10 Hz, which is detrimental for the power reserve of these high-performance oscillators.        